A biosensor is used as a tool for readily determining the quantity of a specific component in a sample solution without diluting and/or stirring the sample solution. Many techniques for overcoming problems of heretofore-used biosensors have been reported.
For example, Japanese Unexamined Patent Publication No. 1991-202764 discloses a method for improving measurement accuracy by adding a hydrophilic polymer to a reaction layer. However, potassium ferricyanides are deposited in the glucose sensor disclosed in Japanese Unexamined Patent Publication No. 1991-202764, the shapes of the obtained reaction parts are not uniform, and therefore the measurement accuracy thereof is insufficient.
There is a technique wherein fine crystalline cellulose is made to coexist in a system having an enzyme and an electronic mediator as a reaction layer (Japanese Unexamined Patent Publication No. 2001-311712). The enzyme sensor disclosed in Japanese Unexamined Patent Publication No. 2001-311712 enhances the uniformity of the thickness of the reaction layer, the precision of the sensor chip, and the performance stability of the chip. However, the fine crystalline cellulose has low solubility in the sample, and therefore it takes time for the fine crystalline cellulose to be satisfactorily dissolved in or mixed with the sample. The measurement thus takes too long. It is presumed that one of the reasons for this problem is that large crystals of potassium hexacyanoferrate (III) grow and the surface area of the reaction layer which can contact the sample become small, and this makes the dispersion and dissolution of the fine crystalline cellulose difficult.
Japanese Unexamined Patent Publication No. 2001-281202 discloses a method wherein a reaction layer is formed by a sublimation method. However, this method requires decompression in the biosensor manufacturing process. This increases costs of facilities, etc., and therefore this method is not suitable for manufacturing a biosensor at low cost. Furthermore, this makes the manufacturing operation complicated, resulting in low productivity.